1. Field of the Invention
The present invention relates to a flame- and smoke-resistant flexible polyurethane foam and a method for producing said flexible polyurethane foam.
2. Description of the Prior Art
In polyurethane foams, a variety of foams, such as flexible, semi-rigid and rigid polyurethane foams can be obtained depending upon the number of functional groups, molecular weight and skeleton structure of polyhydroxyl compound and polyisocyanate to be used and hence the polyurethane foams have a broad application from domestic use to industrial use. However, in order that the polyurethane foams are fully suitable for these uses, it is preferable that the polyurethane foams are provided with flame resistance in view of safety. Recently, the development of polyurethane foams having smoke resistance and a low toxicity as well as flame resistance, has been strongly urged in cushion materials for a variety of vehicles, buildings and interiors.
Heretofore, various attempts have been made with respect to the method for providing the flame resistance for polyurethane foams. For example, an addition of a phosphorus compound, an addition of a halogen compound and a phosphorus compound, an addition of a metal oxide, such as antimony oxide, or use of a reactive flame retardant can provide a certain degree of flame resistance for the polyurethane foams but the polyurethane foams which have been judged as non-flammable by the burning test (ASTM D-1692-59T), are few. Moreover, in these processes, the amount of the flame retardant added is relatively large, for example, 15-25 parts by weight based on 100 parts by weight of polyol, so that the general physical properties of the foam are not only adversely affected but also the emission of smoke upon burning is increased when no flame retardant is used and there is great problem in view of the smoke emission.
Furthermore, it is effective as a means of providing the flame resistance for the polyurethane foams to introduce ring structure having a heat resistance, such as isocyanurate ring structure or imide ring structure into polyurethane molecule, but in this case the resulting foam is apt to become a rigid foam and it has been impossible to obtain a flexible foam, particularly a flexible foam having desirable properties and further a black smoke is liable to be emitted upon burning and such a foam is not desirable.
Namely, in the conventional processes, it has been difficult to provide both the properties of high flame resistance and smoke resistance for the polyurethane foam without adversely affecting the general physical properties of the polyurethane foam.